1. Field of the Invention
The present invention relates to an electroconductive member, a process cartridge, and an electrophotographic image-forming apparatus.
2. Description of the Related Art
In an electrophotographic apparatus, which is an image-forming apparatus employing an electrophotographic system, electroconductive members are used in various applications, for example, as electroconductive rollers, such as a charging roller, a developing roller, and a transferring roller.
When such electroconductive roller is used for a long period of time, dust of, for example, an external additive or toner remaining on a photosensitive member adheres as a contaminant to a surface of the electroconductive roller. For example, in the case of the charging roller, when the contaminant adheres to a surface of the charging roller, its resistance is locally increased at the site where the contaminant adheres, and improper charging occurs at the portion having the increased resistance. As a result, an uneven density of an image due to the contamination occurs in some cases.
In recent years, there have been demands for increases in image quality, speed, and durability of the electrophotographic apparatus. Along with the demands, a particle diameter of the toner tends to be reduced and various kinds of external additives tend to be used. As a result, an amount of the contaminant depositing on the charging member has been increased.
In addition, in recent years, a cleaner-less system (toner recycling system) has been proposed from the viewpoints of simplifying the electrophotographic apparatus and eliminating waste. This system is an electrophotographic process in which a drum cleaner serving as a cleaning unit after a transferring step is eliminated, and transfer residual toner on the photosensitive member after transfer is removed from the photosensitive member by “cleaning simultaneous with development” using a developing apparatus and is recovered and reutilized by the developing apparatus. The cleaning simultaneous with development is a method involving recovering the transfer residual toner remaining on the photosensitive member after transfer during development before proceeding to the next step through the use of a fog-removing bias (fog-removing voltage difference Vback which is a potential difference between a DC voltage to be applied to the developing apparatus and a surface potential of the photosensitive member). As compared to the case where the drum cleaner is present, in the case where a charging roller of a contact charging system is applied to the cleaner-less system, an amount of the contaminant, particularly the toner, remaining on the photosensitive member is dramatically increased, and hence the adhesion of the contaminant to the charging roller becomes a more significant problem.
As a method of reducing the adhesion of the contaminant, such as the external additive or the toner, in Japanese Patent Application Laid-Open No. H06-266206, there is proposed a technique involving coating the surface of the charging member with a fluorine compound, a silicone compound, or the like having an excellent anti-contamination property.
The present invention has been made in view of such technical background, and an object of the present invention is to provide an electroconductive member capable of suppressing adhesion of a contaminant, such as an external additive or toner, independent of use conditions and a use environment. In addition, another object of the present invention is to provide a process cartridge and an electrophotographic image-forming apparatus which are capable of stably forming high-quality electrophotographic images over a long period of time.